Experimental and Computational Assessment of Windage Losses in Rotating Machinery

1996 ◽  
Vol 118 (1) ◽  
pp. 116-122 ◽  
Author(s):  
P. M. Wild ◽  
N. Djilali ◽  
G. W. Vickers
Keyword(s):  
Shear Stress ◽  
Aspect Ratio ◽  
Axial Distribution ◽  
End Effects ◽  
Taylor Vortices ◽  
Functional Relations ◽  
Azimuthal Shear ◽  
Radial Gap ◽  
Gap Width ◽  
Good Agreement

A combined experimental and computational investigation of the flow between a rotating cylinder and a fixed enclosure is presented. The configuration considered is related to the design of a centrifugal desalinator, and includes the flow in the annular as well as in the axial gap regions. The computed flowfield shows significant variations in the axial distribution of the azimuthal shear stress due to the secondary flow associated with Taylor vortices. The averaged azimuthal shear stress (or torque) is however not very sensitive to the number of vortices. Computational results also show that, where the aspect ratio of the annulus (rotor length to radial gap width) is relatively small, this azimuthal variation results in a higher average azimuthal shear stress than for the case where the aspect ratio of the annulus is relatively large. Various functional relations for windage torque of infinite cylinders, developed by other researchers on the basis of power law relations or assuming a log-law velocity distribution, are evaluated. Three such relations are found to be in good agreement with the experimental results when coupled with a correction for end effects. These relations are also the most useful with respect to the design of rotating equipment.

scholarly journals Quantitative Shape-Classification of Misfitting Precipitates during Cubic to Tetragonal Transformations: Phase-Field Simulations and Experiments

Materials ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1373
Author(s):  
Yueh-Yu Lin ◽  
Felix Schleifer ◽  
Markus Holzinger ◽  
Na Ta ◽  
Birgit Skrotzki ◽  
...  
Keyword(s):  
Aspect Ratio ◽  
Phase Field ◽  
Phase Field Model ◽  
Invariant Moments ◽  
Plane Normal ◽  
Plane Shape ◽  
Formation And Evolution ◽  
The Given ◽  
Good Agreement

The effectiveness of the mechanism of precipitation strengthening in metallic alloys depends on the shapes of the precipitates. Two different material systems are considered: tetragonal γ′′ precipitates in Ni-based alloys and tetragonal θ′ precipitates in Al-Cu-alloys. The shape formation and evolution of the tetragonally misfitting precipitates was investigated by means of experiments and phase-field simulations. We employed the method of invariant moments for the consistent shape quantification of precipitates obtained from the simulation as well as those obtained from the experiment. Two well-defined shape-quantities are proposed: (i) a generalized measure for the particles aspect ratio and (ii) the normalized λ2, as a measure for shape deviations from an ideal ellipse of the given aspect ratio. Considering the size dependence of the aspect ratio of γ′′ precipitates, we find good agreement between the simulation results and the experiment. Further, the precipitates’ in-plane shape is defined as the central 2D cut through the 3D particle in a plane normal to the tetragonal c-axes of the precipitate. The experimentally observed in-plane shapes of γ′′-precipitates can be quantitatively reproduced by the phase-field model.

Visual Observations and Torque Measurements in the Taylor Vortex Regime Between Eccentric Rotating Cylinders

1971 ◽  
Vol 93 (1) ◽  
pp. 121-129 ◽  
Author(s):  
P. Castle ◽  
F. R. Mobbs ◽  
P. H. Markho
Keyword(s):  
Outer Cylinder ◽  
Taylor Vortex ◽  
Rotating Cylinders ◽  
Taylor Vortices ◽  
Torque Measurements ◽  
Good Agreement ◽  
Visual Observations

The instability of Taylor vortices in the flow between a stationary outer cylinder and an eccentric rotating inner cylinder has been investigated by visual observations and by torque measurements. It is shown that both a “weak” and “strong” wavy mode of instability can be detected by torque measurements, giving critical Taylor numbers in good agreement with visual observations.

Electrowetting Induced Droplet Generation in T-junctions

2021 ◽  
Author(s):  
Arshia Merdasi ◽  
Ali Moosavi
Keyword(s):  
Shear Stress ◽  
Continuous Phase ◽  
Droplet Breakup ◽  
Droplet Generation ◽  
The Finite Element Method ◽  
Fluidic Channel ◽  
Generation Frequency ◽  
Two Phases ◽  
Breakup Time ◽  
Good Agreement

Abstract In the current study, droplet generation in a T-junction fluidic channel device was studied through using electrowetting actuation with the consideration of different droplet forming regimes. For this purpose, the finite element method (FEM) was used to solve the unsteady Naiver-Stokes equation. In addition, the level set method was applied to capture the interface between two phases. It was shown that there was a good agreement between obtained data and other work during the process of droplet generation in the absence of electrowetting actuation which results in decrease in the size of droplet with increasing the velocity ratios. In shearing regime, the effectiveness of electrowetting on the droplet generation frequency as well as droplet size is visible in a T-junction fluidic channel since after applying voltages, specified with non-dimensional electrowetting numbers of ?=0.5 and 1.2, dispersed phase is pulled out into the oil phase. In fact, with applying the voltage on the top wall, the droplet breakup time was decreased and smaller droplets were produced. Finally, different important parameters such as pressure difference across the interface as well as Shear Stress exerted from the continuous phase shear stress were examined in a detail.

Three-Dimensional Thermocapillary Convection in Open Cylindrical Annuli

2000 ◽  
Author(s):  
Bok-Cheol Sim ◽  
Abdelfattah Zebib
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Critical Frequency ◽  
Thermocapillary Convection ◽  
Three Dimensional ◽  
Time Dependent ◽  
Infinite Layer ◽  
Aspect Ratios ◽  
Temperature Oscillations ◽  
Good Agreement

Abstract Three-dimensional, time-dependent thermocapillary convection in open cylindrical containers is investigated numerically. Results for aspect ratios (Ar) of 1, 2.5, 8, and 16 and a Prandtl number of 6.84 are obtained to compare the results of numerical simulations with ongoing experiments. Convection is steady and axisymmetric at sufficiently low values of the Reynolds number (Re). Transition to oscillatory states occurs at critical values of Re which depend on Ar. With Ar = 1.0 and 2.5, we observe, respectively, 5 and 9 azimuthal wavetrains travelling clockwise at the free surface near the critical Re. With Ar = 8.0 and 16.0, there are substantially more, but pulsating waves near the critical Re. In the case of Ar = 16.0, which approaches the conditions in an infinite layer, our results are in good agreement with linear theory. While the critical Reynolds number decreases with increasing aspect ratio in the case of azimuthal rotating waves, it increases with increasing aspect ratio in the case of azimuthal pulsating waves. The critical frequency of temperature oscillations is found to decrease linearly with increasing Ar. We have also computed supercritical time-dependent states and find that while the frequency increases with increasing Re near the critical region, the frequency of supercritical convection decreases with Re.

scholarly journals Strong and Reversible Adhesion of Interlocked 3D-Microarchitectures

Coatings ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 48 ◽  
Author(s):  
Minho Seong ◽  
Hyun-Ha Park ◽  
Insol Hwang ◽  
Hoon Eui Jeong
Keyword(s):  
Aspect Ratio ◽  
Structural Stability ◽  
High Aspect Ratio ◽  
Three Dimensional ◽  
Normal Direction ◽  
One Dimensional ◽  
Reversible Adhesion ◽  
Adhesion Behavior ◽  
Organic Nanomaterials ◽  
Good Agreement

Diverse physical interlocking devices have recently been developed based on one-dimensional (1D), high-aspect-ratio inorganic and organic nanomaterials. Although these 1D nanomaterial-based interlocking devices can provide reliable and repeatable shear adhesion, their adhesion in the normal direction is typically very weak. In addition, the high-aspect-ratio, slender structures are mechanically less durable. In this study, we demonstrate a highly flexible and robust interlocking system that exhibits strong and reversible adhesion based on physical interlocking between three-dimensional (3D) microscale architectures. The 3D microstructures have protruding tips on their cylindrical stems, which enable tight mechanical binding between the microstructures. Based on the unique 3D architectures, the interlocking adhesives exhibit remarkable adhesion strengths in both the normal and shear directions. In addition, their adhesion is highly reversible due to the robust mechanical and structural stability of the microstructures. An analytical model is proposed to explain the measured adhesion behavior, which is in good agreement with the experimental results.

scholarly journals FLOW DYNAMICS OF WAVES PROPAGATING OVER DIFFERENT PERMEABLE BEDS

2017 ◽  
pp. 35
Author(s):  
Sara Corvaro ◽  
Alessandro Mancinelli ◽  
Maurizio Brocchini
Keyword(s):  
Shear Stress ◽  
Flow Resistance ◽  
Single Layer ◽  
Coastal Engineering ◽  
Flow Dynamics ◽  
Bottom Shear Stress ◽  
Natural Stones ◽  
Wave Height Attenuation ◽  
Rough Beds ◽  
Good Agreement

The analysis of the hydrodynamics over porous media is of interest for many coastal engineering applications as the wave propagation over permeable structures or gravel beaches. The study of a boundary layer evolving over permeable beds is important to a better understanding of the interactions between the flow over and inside the porous medium. An experimental study has been performed to analyze the dynamics produced when waves propagate over two kinds of permeable beds: spheres (regular permeability) and natural stones. For comparative purposes the same analysis has been extended to two rough beds made, respectively, by a single layer of spheres and natural stones. We here focus on the correlation between the wave energy reduction induced by a porous bed and the flow resistance. An experimental law for the prediction of the friction factor is found by using the log-fit method in analogy to that reported in Dixen et al. (2008) for rough beds. Moreover, inspection of the turbulent velocity components allows one to evaluate the bottom shear stress. The latter analysis has been performed for different permeable beds (regular and irregular beds). A good agreement between the bottom shear stress behavior and the wave height attenuation over rough and permeable beds (Corvaro et al. 2010 and Corvaro et al. 2014a) has been observed.

The Mixing Length Derived from Kármán’s Similarity Hypothesis

1973 ◽  
Vol 24 (1) ◽  
pp. 71-76 ◽  
Author(s):  
Michio Nishioka ◽  
Shūsuke Iida
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Reasonable Agreement ◽  
Diffusion Constant ◽  
Turbulent Shear ◽  
Appreciable Effect ◽  
Mixing Length ◽  
Similarity Hypothesis ◽  
Turbulent Shear Stress ◽  
Good Agreement

SummaryFrom Kármán’s similarity hypothesis, we derive the equation which describes the mixing length in terms of the turbulent shear stress. For a boundary layer with linear stress distribution, the equation is in reasonable agreement with Bradshaw’s measurements. For a boundary layer with injection, it is shown that injection has an appreciable effect upon the mixing length when (vw/2) /(τ/ρ)1/2becomes comparable to the Kármán constant. Close similarity is also pointed out between the hypotheses due to Kármán and Townsend. Moreover, the diffusion constant in Townsend’s hypothesis is determined to be 0.25, which is in good agreement with the value 0.2 obtained by Townsend from one experiment.

scholarly journals Steady supercritical Taylor vortex flow

1973 ◽  
Vol 58 (3) ◽  
pp. 547-560 ◽  
Author(s):  
J. E. Burkhalter ◽  
E. L. Koschmieder
Keyword(s):  
Vortex Flow ◽  
Finite Cylinder ◽  
Taylor Vortex ◽  
End Effects ◽  
Taylor Vortices ◽  
Taylor Vortex Flow ◽  
Critical Wavelength ◽  
Very High ◽  
Long Cylinder

Experiments studying steady supercritical Taylor vortex flow have been made using pairs of long cylinders with two different radius ratios, three fluids of different viscosities and three different end boundaries for the fluid column. The emphasis in these experiments is on the determination of the wavelength of the Taylor vortices and the size of the end rings. The wavelength which one measures in a finite cylinder differs from the wavelengths found theoretically for infinitely long cylinders. Provided that the end effects were properly taken into account, the wavelength of singly periodic Taylor vortices in aninfinitely long cylinder was found to remain constant between T/Tc = 1 and T/Tc, ≈ 80 in experiments with radius ratios η = 0·505 and η = 0·727. Further studies of Taylor vortex flow at very high Taylor numbers, where the vortices are either doubly periodic or truly turbulent, showed that the wavelength increases under these conditions. However, the observed wavelengths were no longer unique but distributed statistically around a wavelength larger than the critical wavelength.

Modeling and Optimization of Gaseous Slip Flow Forced Convection in Rectangular Microducts Using Particle Swarm Optimization Algorithm

2018 ◽  
Author(s):  
Waqar A. Khan ◽  
Nawaf N. Hamadneh
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Particle Swarm Optimization ◽  
Aspect Ratio ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Particle Swarm Optimization Algorithm ◽  
Slip Flow ◽  
Swarm Optimization ◽  
Gaseous Slip Flow

In this study, pressure driven gaseous slip flow is investigated in microducts of rectangular cross-section. The range of Knudsen numbers Kn in the flow regime is taken as 0.001 ≤ Kn ≤ 0.1 and aspect ratio is taken as 0 ≤ ε ≤ 1. To incorporate rarefaction effects, the effects of slip velocity and temperature jump boundary conditions are taken in to account. The dimensionless momentum and energy equations are solved using MATLAB to obtain the dimensionless velocity and temperature gradients for different values of Knudsen numbers and aspect ratio. Using these gradients, the dimensionless shear stress and heat transfer rate are obtained numerically. The numerical solution can be validated for the special cases when there is no slip (continuum flow), ε = 0 (parallel plates) and ε = 1 (square microducts). An artificial neural network is used to develop separate models for dimensionless shear stress and heat transfer rate and particle swarm optimization algorithm is used to obtain optimum values for both parameters. Using these results, minimum dimensionless shear stress and maximum heat transfer rate can be determined in the microducts under consideration in the slip flow regime. The optimal values of P0 and Nu are found when ε = 1 and Kn = 0.001.

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